echevy, "Is the RS232 output normally affected by noise from the drive system?"
If you can get a scope you may be able to tell, even then it can be hard to catch transient occurrences. However, motor drive can make incredibly loud electrical noise, I scope set on peak detect or sample (as opposed to a ji resolution mode of acquisition) will make the noise persist on screen and you can see it and gauge the levels. RS232 is a TTL signal which is not great for noise protection. If you have a choice triggering on signals like a serial square wave looking for the falling edge is much better. Doubt if you have that kind of control. Anyway, if the noise on the high of the square wave is more than a couple volts it can make for false triggering even with falling edge detection. That was just background not a solution. If people experienced with your particular combination of motor drive and laptop can function without noise then you can possibly sort it out. Absent that you will have to guess if it is possible to succeed You need to be very rigorous with your wiring if it is indeed a noise problem. No twisted together wires or wire nuts, only good solder and crimp joints. No stray braided shields popping out to brush against anything. All must be very neat and tidy if you are trying to solve a pernicious noise problem. You will want to segregate any power conductors from any data conductors. Don't let them be draped around each other even with shielding. There are two main ways that wire can cause noise to couple to the data. Anytime there is a single coil of a power conductor (actually even a quarter coil can do this) if the voltage rises or falls in the coil it can couple to a wire that lies across or near the coil by inductive coupling. Many motor drives have very large voltage gradients in their wires which makes them great radiating antenna. The second method is whenever power and data wires lay parallel to each other then they couple capacitively. NEVER EVER run power and data together in the same cable or conduit. Segregate than completely. Isolate them in separate conductive shields or conduits (ferrous is best). If power and data must cross each other make the crossing flat, straight and perpendicular. out some distance between them. If power and data have to route to the same component (like a motor drive) try get then to come from opposite directions and no crossing or looping. I recommend the USB to serial converters with chipsets by FTDI. Keyspan is popular, but I think FTDI is a little better. The cut rate stuff like Sabrent (COmpUSA/Tigerdirect) with the Prolific chipset is not as good and there is no tech support. The outlet for FTDI is called EasySync. A USB to Serial cable is not too expensive, but more than $10. I come by this understanding first hand. This can be hard to solve. I have work for years reducing the noise of one system I have to live with. I have not actually had trouble with noise on the USB to serial, only on other data streams. I am sure though that it can happen. RS 485 was devised because RS 242 sucks pretty bad. If there is a connection to AC ground on both the EV and the laptop, that can be a path for large common mode noise. Run the laptop on its battery and don't let it touch things that may have a path to the EV. Another thing to try is varying the baud rate. I would be curious if you read the meter, but not actually reading the EV, but in the vicinity if you would get squirrely data. I probably should have reviewed the whole thread before answering, but I though my general view of noise control might be useful. Good luck, BentMike On Mon, Nov 11, 2013 at 9:33 PM, Lee Hart <[email protected]> wrote: > echevy wrote: > >> The ultimate goal was to get the emeter working so that I can capture the >> serial output to put in a spread sheet for a picture of the pack current >> and >> voltage as I drive. This seems to be working, however I'm getting some >> garbled lines and stray characters. I'm using RealTerm to do the capture. >> I've got a USB to RS232 converter that uses one of the more popular chips >> for this purpose. The drivers are up to date. I'm running on a little >> netbook on batteries as I drive around. >> >> Is the RS232 output normally affected by noise from the drive system? >> > > I haven't seen it affected by noise. But I *have* had lots of problems > with Windows missing characters. The only way I've been able to receive > *all* of the data without any missing characters is by capturing the data > from a DOS program. > > I normally use a little QuickBASIC program I wrote. It receives the data > bursts every 1 second, and condenses them down. If a particular value > hasn't changed, it doesn't write it to disk. Instead, it only writes them > when there is enough of a change. This vastly reduces the size of the data > files, and makes them far easier to handle with Excel etc. > > -- > ICEs have the same problem as lightbulbs. Why innovate and make > better ones when the current ones burn out often enough to keep > you in business? -- Hunter Cressall > -- > Lee Hart, http://www.sunrise-ev.com/LeesEVs.htm, ebay# 271318702449 > > _______________________________________________ > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > http://lists.evdl.org/listinfo.cgi/ev-evdl.org > For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/ > group/NEDRA) > > -- Put this question to yourself: should I use everyone else to attain happiness, or should I help others gain happiness? *Dalai Lama * Tell me what it is you plan to do WIth your one wild and precious life? Mary Oliver, "The summer day." To invent, you need a good imagination and a pile of junk. Thomas A. Edison<http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html> A public-opinion poll is no substitute for thought. *Warren Buffet* Michael E. 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